I get it all the time when, no, I'm not -that- mixed. I'm the standard American "Black with some other stuff thrown in" but, its assumed because my skin is, uh...peanut butter colored (not even "light" by our stringent definitions) and I am a 3c with hazel eyes and a smallish nose I must be biracial. They act shocked when I'm like "Nope. Black. Blackity black black. Problem?"